Methods and apparatus for cleaning substrates

ABSTRACT

A method for effectively cleaning vias (20034), trenches (20036) or recessed areas on a substrate (20010) using an ultra/mega sonic device (1003, 3003, 16062, 17072), comprising: applying liquid (1032) into a space between a substrate (20010) and an ultra/mega sonic device (1003, 3003, 16062, 17072); setting an ultra/mega sonic power supply at frequency f1 and power P1 to drive said ultra/mega sonic device (1003, 3003, 16062, 17072); after the ratio of total bubbles volume to volume inside vias (20034), trenches (20036) or recessed areas on the substrate (20010) increasing to a first set value, setting said ultra/mega sonic power supply at frequency f2 and power P2 to drive said ultra/mega sonic device (1003, 3003, 16062, 17072); after the ratio of total bubbles volume to volume inside the vias (20034), trenches (20036) or recessed areas reducing to a second set value, setting said ultra/mega sonic power supply at frequency f1 and power P1 again; repeating above steps till the substrate (20010) being cleaned.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application claiming priority under 35U.S.C. § 120 to U.S. patent application Ser. No. 16/334,703, entitledMETHODS AND APPARATUS FOR CLEANING SUBSTRATES, filed Mar. 19, 2019,which is a U.S. National Stage Entry under 35 U.S.C. § 371 ofInternational Patent Application No. PCT/CN2016/0993003, filed Sep. 19,2016 and titled METHODS AND APPARATUS FOR CLEANING SUBSTRATES, theentire disclosures of which are hereby incorporated by reference herein.

FIELD OF THE INVENTION

The present invention generally relates to method and apparatus forcleaning substrate. More particularly, relates to controlling the bubblecavitation generated by ultra or mega sonic device during the cleaningprocess to achieve a stable or controlled cavitation on the entiresubstrate, which removes fine particles efficiently in vias, trenches orrecessed areas with high aspect ratio.

BACKGROUND

Semiconductor devices are manufactured or fabricated on semiconductorsubstrates using a number of different processing steps to createtransistor and interconnection elements. Recently, the transistors arebuilt from two dimensions to three dimensions such as finFET transistorsand 3D NAND memory. To electrically connect transistor terminalsassociated with the semiconductor substrate, conductive (e.g., metal)trenches, vias, and the like are formed in dielectric materials as partof the semiconductor device. The trenches and vias couple electricalsignals and power between transistors, internal circuit of thesemiconductor devices, and circuits external to the semiconductordevice.

In forming the finFET transistors and interconnection elements on thesemiconductor substrate may undergo, for example, masking, etching, anddeposition processes to form the desired electronic circuitry of thesemiconductor devices. In particular, multiple masking and plasmaetching step can be performed to form a pattern of finFET, 3D NAND flashcell and or recessed areas in a dielectric layer on a semiconductorsubstrate that serve as fin for the transistor and or trenches and viasfor the interconnection elements. In order to removal particles andcontaminations in fin structure and or trench and via post etching orphoto resist ashing, a wet cleaning step is necessary. Especially, whendevice manufacture node migrating to 14 or 16 nm and beyond, the sidewall loss in fin and or trench and via is crucial for maintaining thecritical dimension. In order to reduce or eliminate the side wall loss,it is important to use moderate, dilute chemicals, or sometimede-ionized water only. However, the dilute chemical or de-ionized waterusually is not efficient to remove the particles in the fin structure,3D NAND hole and or trench and via. Therefore the mechanical force suchas ultra or mega sonic is needed in order to remove those particlesefficiently. Ultra sonic or mega sonic wave will generate bubblecavitation which applies mechanical force to substrate structure, theviolent cavitation such as transit cavitation or micro jet will damagethose patterned structures. To maintain a stable or controlledcavitation is key parameters to control the mechanical force within thedamage limit and at the same time efficiently to remove the particles.In the 3D NAND hole structure, the transit cavitation may not damage thehole structure, but however, the bubble cavitation saturated inside holewill stop or reduce the cleaning effects.

Mega sonic energy coupled with nozzle to clean semiconductor wafer isdisclosed in U.S. Pat. No. 4,326,553. The fluid is pressurized and megasonic energy is applied to the fluid by a mega sonic transducer. Thenozzle is shaped to provide a ribbon-like jet of cleaning fluidvibrating at ultra/mega sonic frequencies for the impingement on thesurface.

A source of energy vibrates an elongated probe which transmits theacoustic energy into the fluid is disclosed in U.S. Pat. No. 6,039,059.In one arrangement, fluid is sprayed onto both sides of a wafer while aprobe is positioned close to an upper side. In another arrangement, ashort probe is positioned with its end surface close to the surface, andthe probe is moved over the surface as wafer rotates.

A source of energy vibrates a rod which rotates around it axis parallelto wafer surface is disclosed in U.S. Pat. No. 6,843,257 B2. The rodsurface is etched to curve groves, such as spiral groove.

It is needed to have a better method for controlling the bubblecavitation generated by ultra or mega sonic device during the cleaningprocess to achieve a stable or controlled cavitation on the entiresubstrate, which removes fine particles efficiently in vias, trenches orrecessed areas with high aspect ratio.

SUMMARY

One method of the present invention is to achieve a damage freeultra/mega-sonic cleaning on a wafer with patterned structure bymaintaining a stable bubble cavitation. The stable bubble cavitation iscontrolled by setting a sonic power supply with power P₁ at a timeinterval shorter than τ₁, and setting the sonic power supply with powerP₂ at a time interval longer than τ₂, and repeat above steps till thewafer is cleaned, where power P₂ is equal to zero or much smaller thanpower P₁, τ₁ is a time interval that the temperature inside bubbleraises to a critical implosion temperature; and τ₂ is a time intervalthat the temperature inside bubble falls down to a temperature muchlower than the critical implosion temperature.

Another method of the present invention is to achieve a damage freeultra/mega sonic cleaning on a wafer with patterned structure bymaintaining a stable bubble cavitation. The stable bubble cavitation iscontrolled by setting a sonic power supply with frequency f₁ at a timeinterval shorter than τ₁, and setting the sonic power supply withfrequency f₂ at a time interval longer than τ₂, and repeat above stepstill the wafer is cleaned, where f₂ is much higher than f₁, better to be2 times or 4 times higher, τ₁ is a time interval that the temperatureinside bubble raises to a critical implosion temperature; and τ₂ is atime interval that the temperature inside bubble falls down to atemperature much lower than the critical implosion temperature.

Another method of the present invention is to achieve a damage freeultra/mega-sonic cleaning on a wafer with patterned structure bymaintaining a stable bubble cavitation with bubble size less than spacein patterned structure. The stable bubble cavitation with bubble sizeless than space in patterned structure is controlled by setting a sonicpower supply at power P₁ for a time interval shorter than τ₁, andsetting the sonic power supply at power P₂ for a time interval longerthan τ₂, and repeat above steps till the wafer is cleaned, where P₂ isequal to zero or much smaller than P₁, τ₁ is a time interval that thebubble size increases to a critical size equal to or larger than thespace in patterned structures; and τ₂ is a time interval that the bubblesize decreases to a value much smaller than the space in patternedstructure.

Another method of the present invention is to achieve a damage freeultra/mega-sonic cleaning on a wafer with patterned structure bymaintaining a stable bubble cavitation with bubble size less than spacein patterned structure. The stable bubble cavitation with bubble sizeless than space in patterned structure is controlled by setting a sonicpower supply with frequency f₁ for a time interval shorter than τ₁, andsetting the sonic power supply with frequency f₂ for a time intervallonger than τ₂, and repeat above steps till the wafer is cleaned, wheref₂ is much higher than f₁, better to be 2 times or 4 times higher, τ₁ isa time interval that the bubble size increases to a critical size equalto or larger than the space in patterned structures; and τ₂ is a timeinterval that the bubble size decreases to a value much smaller than thespace in patterned structure.

One method of the present invention is to achieve an effectiveultra/mega-sonic cleaning on a substrate with features of deep holes bymaintaining a non-saturated bubble cavitation. The non-saturated bubblecavitation is controlled by setting a sonic power supply with power P₁at a time interval shorter than τ₁, and setting the sonic power supplywith power P₂ at a time interval longer than τ₂, and repeating abovesteps till the substrate is cleaned, where power P₂ is equal to zero ormuch smaller than power P₁, τ₁ is a time interval that the cavitation orbubble density inside the deep hole raises to saturated status; and τ₂is a time interval that bubble density falls down to a level much lowerthan the saturated status.

Another method of the present invention is to achieve an effectiveultra/mega-sonic cleaning on a substrate with features of deep holes bymaintaining a non-saturated bubble cavitation. The non-saturated bubblecavitation is controlled by setting a sonic power supply with frequencyf₁ at a time interval shorter than τ₁, and setting the sonic powersupply with frequency f₂ at a time interval longer than τ₂, andrepeating above steps till the substrate is cleaned, where f₂ is muchhigher than f₁, better to be 2 times or 4 times higher, τ₁ is a timeinterval that the cavitation or bubble density inside the deep holeraises to saturated status; and τ₂ is a time interval that bubbledensity falls down to a level much lower than the saturated status.

One method of the present invention is to achieve an effectiveultra/mega-sonic cleaning on a substrate with features of deep holes bymaintaining a certain size of bubble in cavitation status. The certainsize of bubble in cavitation status is controlled by setting a sonicpower supply with power P₁ at a time interval shorter than τ₁, andsetting the sonic power supply with power P₂ at a time interval longerthan τ₂, and repeating above steps till the substrate is cleaned, wherepower P₂ is equal to zero or much smaller than power P₁, τ₁ is a timeinterval that the cavitation or bubble density inside the deep holeraises to saturated status; and τ₂ is a time interval that bubble sizefalls down to a level much smaller than the certain size.

Another method of the present invention is to achieve an effectiveultra/mega-sonic cleaning on a substrate with features of deep holes bymaintaining a certain size of bubble in cavitation status. The certainsize of bubble in cavitation status is controlled by setting a sonicpower supply with frequency f₁ at a time interval shorter than τ₁, andsetting the sonic power supply with frequency f₂ at a time intervallonger than τ₂, and repeating above steps till the substrate is cleaned,where f₂ is much higher than f₁, better to be 2 times or 4 times higher,τ₁ is a time interval that the cavitation or bubble density inside thedeep hole raises to saturated status; and τ₂ is a time interval thatbubble size falls down to a level much smaller than the certain size.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1B depict an exemplary wafer cleaning apparatus usingultra/mega sonic device;

FIGS. 2A-2G depict variety of shape of ultra/mega sonic transducers;

FIG. 3 depicts bubble cavitation during wafer cleaning process;

FIGS. 4A-4B depict a transit cavitation damaging patterned structure ona wafer during cleaning process;

FIGS. 5A-5C depict thermal energy variation inside bubble duringcleaning process;

FIGS. 6A-6C depict an exemplary wafer cleaning method;

FIGS. 7A-7C depict another exemplary wafer cleaning method;

FIGS. 8A-8D depict another exemplary wafer cleaning method;

FIGS. 9A-9D depict another exemplary wafer cleaning method;

FIGS. 10A-10B depict another exemplary wafer cleaning method;

FIGS. 11A-11B depict another exemplary wafer cleaning method;

FIGS. 12A-12B depict another exemplary wafer cleaning method;

FIGS. 13A-13B depict another exemplary wafer cleaning method;

FIGS. 14A-14B depict another exemplary wafer cleaning method;

FIGS. 15A-15C depict a stable cavitation damaging patterned structure ona wafer during cleaning process;

FIG. 16 depicts another exemplary wafer cleaning apparatus usingultra/mega sonic device; and

FIG. 17 depicts an exemplary wafer cleaning apparatus using ultra/megasonic device;

FIGS. 18A-18C depict another exemplary wafer cleaning method;

FIG. 19 depicts another exemplary wafer cleaning method;

FIG. 20A to FIG. 20D depict bubbles in the status of below thesaturation point in the feature of vias or trenches;

FIG. 20E to FIG. 20H depict the size of bubbles expanded by theultra/mega sonic device to result in the ratio R of total bubbles volumeV_(B) to the volume of via, trench or recessed space V_(VTR) beingclosed to or above the saturation point;

FIG. 20I and FIG. 20J depict the size of bubbles expanded by theultra/mega sonic device within a limitation to result in the ratio R oftotal bubbles volume V_(B) to the volume of via, trench or recessedspace V_(VTR) being much below the saturation point;

FIGS. 21A-21D depict an exemplary substrate cleaning method;

FIGS. 22A-22D depict another exemplary substrate cleaning method;

FIGS. 23A-23C depict another exemplary substrate cleaning method.

DETAILED DESCRIPTION

FIGS. 1A to 1B show a wafer cleaning apparatus using a ultra/mega sonicdevice. The wafer cleaning apparatus consists of wafer 1010, wafer chuck1014 being rotated by rotation driving mechanism 1016, nozzle 1012delivering cleaning chemicals or de-ionized water 1032, and ultra/megasonic device 1003 and ultra/mega sonic power supply. The ultra/megasonic device 1003 further consists of piezoelectric transducer 1004acoustically coupled to resonator 1008. Transducer 1004 is electricallyexcited such that it vibrates and the resonator 1008 transmits highfrequency sound energy into liquid. The bubble cavitation generated bythe ultra/mega sonic energy oscillates particles on wafer 1010.Contaminants are thus vibrated away from the surfaces of the wafer 1010,and removed from the surfaces through the flowing liquid 1032 suppliedby nozzle 1012.

FIGS. 2A to 2G show top view of ultra/mega sonic devices according tothe present invention. Ultra/mega sonic device 1003 shown in FIG. 1 canbe replaced by different shape of ultra/mega sonic devices 3003, i.e.triangle or pie shape as shown in FIG. 2A, rectangle as shown in FIG.2B, octagon as shown in FIG. 2C, elliptical as shown in FIG. 2D, halfcircle as shown in FIG. 2E, quarter circle as shown in FIG. 2F, andcircle as shown in FIG. 2G.

FIG. 3 shows a bubble cavitation during compression phase. The shape ofbubbler is gradually compressed from a spherical shape A to an appleshape G, finally the bubble reaches to an implosion status I and forms amicro jet. As shown in FIGS. 4A and 4B, the micro jet is very violent(can reaches a few thousands atmospheric pressures and a few thousands °C.), which can damage the fine patterned structure 4034 on thesemiconductor wafer 4010, especially when the feature size t shrinks to70 nm and smaller.

FIGS. 5A to 5C show simplified model of bubble cavitation according tothe present invention. As sonic positive pressure acting on the bubble,the bubble reduces its volume. During this volume shrinking process, thesonic pressure P_(M) did a work to the bubble, and the mechanical workconverts to thermal energy inside the bubble, therefore temperature ofgas and/or vapor inside bubble increases.

The idea gas equation can be expressed as follows:p ₀ v ₀ /T ₀ =pv/T  (1),

where, p₀ is pressure inside bubbler before compression, v₀ initialvolume of bubble before compression, T₀ temperature of gas insidebubbler before compression, p is pressure inside bubbler in compression,v volume of bubble in compression, T temperature of gas inside bubblerin compression.

In order to simplify the calculation, assuming the temperature of gas isno change during the compression or compression is very slow andtemperature increase is cancelled by liquid surrounding the bubble. Sothat the mechanical work w_(m) did by sonic pressure P_(M) during onetime of bubbler compression (from volume N unit to volume 1 unit orcompression ratio=N) can be expressed as follows:

$\begin{matrix}{w_{m} = {{\int_{0}^{{x0} - 1}{pSdx}} = {{\int_{0}^{{x0} - 1}{\left( {{S\left( {x_{0}p_{0}} \right)}/\left( {x_{0} - x} \right)} \right){dx}}} = {{{Sx}_{0}p_{0}{\int_{0}^{{x0} - 1}{{dx}/\left( {x_{0} - x} \right)}}} = {{{{- {Sx}_{0}}p_{0}{\ln\left( {x_{0} - x} \right)}}|_{0}^{{x\; 0} - 1}} = {{Sx}_{0}p_{0}{\ln\left( x_{0} \right)}}}}}}} & (2)\end{matrix}$

Where, S is area of cross section of cylinder, x₀ the length of thecylinder, p₀ pressure of gas inside cylinder before compression. Theequation (2) does not consider the factor of temperature increase duringthe compression, so that the actual pressure inside bubble will behigher due to temperature increase. Therefore the actual mechanical workconducted by sonic pressure will be larger than that calculated byequation (2).

If assuming all mechanical work did by sonic pressure is partiallyconverted to thermal energy and partially converted mechanical energy ofhigh pressure gas and vapor inside bubble, and such thermal energy isfully contributed to temperature increase of gas inside of bubbler (noenergy transferred to liquid molecules surrounding the bubble), andassuming the mass of gas inside bubble staying constant before and aftercompression, then temperature increase ΔT after one time of compressionof bubble can be expressed in the following formula:ΔT=Q/(mc)=βw _(m)/(mc)=βSx ₀ p ₀ ln(x ₀)/(mc)  (3)where, Q is thermal energy converted from mechanical work, β ratio ofthermal energy to total mechanical works did by sonic pressure, m massof gas inside the bubble, c gas specific heat coefficient. Substitutingβ=0.65, S=1E-12 m², x₀=1000 μm=1E-3 m (compression ratio N=1000), p₀=1kg/cm²=1E4 kg/m², m=8.9E-17 kg for hydrogen gas, c=9.9E3 J/(kg ° k) intoequation (3), then ΔT=50.9° k.

The temperature T₁ of gas inside bubbler after first time compressioncan be calculated asT ₁ =T ₀ +ΔT=20° C.+50.9° C.=70.9° C.  (4)

When the bubble reaches the minimum size of 1 micron as shown in FIG.5B. At such a high temperature, of cause some liquid moleculessurrounding bubble will evaporate. After then, the sonic pressure becomenegative and bubble starts to increase its size. In this reverseprocess, the hot gas and vapor with pressure P_(G) will do work to thesurrounding liquid surface. At the same time, the sonic pressure P_(M)is pulling bubble to expansion direction as shown in FIG. 5C, thereforethe negative sonic pressure P_(M) also do partial work to thesurrounding liquid too. As the results of the joint efforts, the thermalenergy inside bubble cannot be fully released or converted to mechanicalenergy, therefore the temperature of gas inside bubble cannot cool downto original gas temperature T₀ or the liquid temperature. After thefirst cycle of cavitation finishes, the temperature T₂ of gas in bubblewill be somewhere between T₀ and T₁ as shown in FIG. 6B. Or T₂ can beexpressed asT ₂ =T1−δT=T ₀ +ΔT−δT  (5)

Where δT is temperature decrease after one time of expansion of thebubble, and δT is smaller than ΔT.

When the second cycle of bubble cavitation reaches the minimum bubblesize, the temperature T3 of gas and or vapor inside bubbler will beT3=T2+ΔT=T ₀ +ΔT−δT+ΔT=T ₀+2ΔT−δT  (6)

When the second cycle of bubble cavitation finishes, the temperature T4of gas and/or vapor inside bubbler will beT4=T3−δT=T ₀+2ΔT−δT−δT=T ₀+2ΔT−2δT  (7)

Similarly, when the nth cycle of bubble cavitation reaches the minimumbubble size, the temperature T_(2n-1) of gas and or vapor inside bubblerwill beT _(2n-1) =T ₀ +nΔT−(n−1)δT  (8)

When the nth cycle of bubble cavitation finishes, the temperature T_(2n)of gas and/or vapor inside bubbler will beT _(2n) =T ₀ +nΔT−nδT=T ₀ +n(ΔT−δT)  (9)

As cycle number n of bubble cavitation increase, the temperature of gasand vapor will increase, therefore more molecules on bubble surface willevaporate into inside of bubble 6082 and size of bubble 6082 willincrease too, as shown in FIG. 6C. Finally the temperature inside bubbleduring compression will reach implosion temperature T_(i) (normallyT_(i) is as high as a few thousands ° C.), and violent micro jet 6080forms as shown in FIG. 6C.

From equation (8), implosion cycle number n_(i) can be written asfollowing:n _(i)=(T _(i) −T ₀ −ΔT)/(ΔT−δT)+1  (10)

From equation (10), implosion time τ_(i), can be written as following:

$\begin{matrix}{\tau_{i} = {{n_{i}t_{1}} = {{t_{1}\left( {{\left( {T_{i} - T_{0} - {\Delta T}} \right)/\left( {{\Delta T} - {\delta T}} \right)} + 1} \right)} = {{n_{i}/f_{1}} = {\left( {{\left( {T_{i} - T_{0} - {\Delta T}} \right)/\left( {{\Delta T} - {\delta T}} \right)} + 1} \right)/f_{1}}}}}} & (11)\end{matrix}$

Where, t₁ is cycle period, and f₁ frequency of ultra/mega sonic wave.

According to formulas (10) and (11), implosion cycle number n_(i) andimplosion time τ_(i), can be calculated. Table 1 shows calculatedrelationships among implosion cycle number n_(i), implosion time τ_(i)and (ΔT−δT), assuming Ti=3000° C., ΔT=50.9° C., T₀=20° C., f₁=500 KHz,f₁=1 MHz, and f₁=2 MHz.

TABLE 1 ΔT - δT (° C.) 0.1 1 10 30 50 n_(i) 29018 2903 291 98 59 τ_(i)(ms) 58.036 5.806 0.582 0.196 0.118 f₁ = 500 KHz τ_(i) (ms) 29.018 2.9030.291 0.098 0.059 f₁ = 1 MHz τ_(i) (ms) 14.509 1.451 0.145 0.049 0.029f₁ = 2 MHz

In order to avoid damage to patterned structure on wafer, a stablecavitation must be maintained, and the bubble implosion or micro jetmust be avoided. FIGS. 7A to 7C shows a method to achieve a damage freeultra or mega-sonic cleaning on a wafer with patterned structure bymaintaining a stable bubble cavitation according to the presentinvention. FIG. 7A shows waveform of power supply outputs, and FIG. 7Bshows the temperature curve corresponding to each cycle of cavitation,and FIG. 7C shows the bubble size expansion during each cycle ofcavitation. Operation process steps to avoid bubble implosion accordingto the present invention are disclosed as follows:

Step 1: Put ultra/mega sonic device adjacent to surface of wafer orsubstrate set on a chuck or tank;

Step 2: Fill chemical liquid or gas (hydrogen, nitrogen, oxygen, or CO₂)doped water between wafer and the ultra/mega sonic device;

Step 3: Rotate chuck or oscillate wafer;

Step 4: Set power supply at frequency f₁ and power P₁;

Step 5: Before temperature of gas and vapor inside bubble reachesimplosion temperature T_(i), (or time reach τ₁<τ_(i) as being calculatedby equation (11)), set power supply output to zero watts, therefore thetemperature of gas inside bubble start to cool down since thetemperature of liquid or water is much lower than gas temperature.

Step 6: After temperature of gas inside bubble decreases to roomtemperature T₀ or time (zero power time) reaches τ₂, set power supply atfrequency f₁ and power P₁ again.

Step 7: repeat Step 1 to Step 6 until wafer is cleaned.

In step 5, the time τ₁ must be shorter than τ_(i) in order to avoidbubble implosion, and τ_(i) can be calculated by using equation (11).

In step 6, the temperature of gas inside bubble is not necessary to becooled down to room temperature or liquid temperature; it can be certaintemperature above room temperature or liquid temperature, but better tobe significantly lower than implosion temperature T_(i).

According to equations 8 and 9, if (ΔT−δT) can be known, the can becalculated. But in general, (ΔT−δT) is not easy to be calculated ormeasured directly. The following method can determine the implosion timeτ_(i) experimentally.

Step 1: Based on Table 1, choosing 5 different time τ₁ as design ofexperiment (DOE) conditions,

Step 2: choose time τ₂ at least 10 times of τ₁, better to be 100 timesof τ₁ at the first screen test

Step 3: fix certain power P₀ to run above five conditions cleaning onspecific patterned structure wafer separately. Here, P₀ is the power atwhich the patterned structures on wafer will be surely damaged whenrunning on continuous mode (non-pulse mode).

Step 4: Inspect the damage status of above five wafers by SEMS or waferpattern damage review tool such as AMAT SEM vision or Hitachi IS3000,and then the implosion time can be located in certain range.

Step 1 to 4 can be repeated again to narrow down the range of implosiontime τ_(i). After knowing the implosion time τ_(i), the time τ₁ can beset at a value smaller than 0.5τ_(i) for safety margin. One example ofexperimental data is described as following.

The patterned structures are 55 nm poly-silicon gate lines. Ultra/megasonic wave frequency was 1 MHz, and ultra/mega-sonic device manufacturedby Prosys was used and operated in a gap oscillation mode (disclosed byPCT/CN2008/073471) for achieving better uniform energy dose within waferand wafer to wafer. Other experimental parameters and final patterndamage data are summarized in Table 2 as follows:

TABLE 2 CO₂ Power Number conc. Process Density of Wafer (18 Time (Watts/Cycle τ₁ τ₂ Damage ID μs/cm) (sec) cm2) Number (ms) (ms) Sites #1 18 600.1 2000 2   18 1216 #2 18 60 0.1  100 0.1 0.9   0

It was clear that the τ_(i)=2 ms (or 2000 cycle number) introduced asmany as 1216 damage sites to patterned structure with 55 nm featuresize, but that the τ_(i)=0.1 ms (or 100 cycle number) introduced zero(0) damage sites to patterned structure with 55 nm feature size. So thatthe τ_(i) is some number between 0.1 ms and 2 ms, more detail tests needto be done to narrow its range. Obviously, the cycle number related toultra or mega sonic power density and frequency, the larger the powerdensity, the less the cycle number; and the lower the frequency, theless the cycle number. From above experimental results, we can predictthat the damage-free cycle number should be smaller than 2,000, assumingthe power density of ultra or mega sonic wave is larger than 0.1wattsorcm², and frequency of ultra or mega sonic wave is equal to orless than 1 MHz. If the frequency increases to a range larger than 1 MHzor power density is less than than 0.1 watts/cm², it can be predictedthat the cycle number will increase.

After knowing the time τ₁, then the time T₂ can be shorten based onsimilar DEO method described above, i.e. fix time τ₁, gradually shortenthe time τ₂ to run DOE till damage on patterned structure beingobserved. As the time τ₂ is shorten, the temperature of gas and or vaporinside bubbler cannot be cooled down enough, which will gradually shiftaverage temperature of gas and vapor inside bubbler up, eventually itwill trigger implosion of bubble. This trigger time is called criticalcooling time. After knowing critical cooling time τ_(c), the time τ₂ canbe set at value larger than 2τ_(c) for the same reason to gain safetymargin.

FIGS. 8A to 8D show another embodiment of wafer cleaning method using aultra/mega sonic device according to the present invention. The methodis similar to that shown in FIG. 7A, except in step 4 setting ultra/megasonic power supply at frequency f₁ and power with changing amplitude ofwaveform. FIG. 8A shows another cleaning method of setting ultra/megasonic power at frequency f₁ and power with increasing amplitude ofwaveform in step 4. FIG. 8B shows another cleaning method of settingultra/mega sonic power supply at frequency f₁ and power with decreasingamplitude of waveform in step 4. FIG. 8C shows another cleaning methodof setting ultra/mega sonic power supply at frequency f₁ and power withdecreasing first and increasing later amplitude of waveform in step 4.FIG. 8D shows further another cleaning method of setting ultra/megasonic power at frequency f₁ and power with increasing first anddecreasing later amplitude of waveform in step 4.

FIGS. 9A to 9D show another embodiment of wafer cleaning method using aultra/mega sonic device according to the present invention. The methodis similar to that shown in FIG. 7A, except in step 4 setting ultra/megasonic power supply at changing frequency. FIG. 9A shows another cleaningmethod of setting ultra/mega sonic power supply at frequency f₁ firstthen frequency f₃ later, f₁ is higher than f₃ in step 4. FIG. 9B showsanother cleaning method of setting ultra/mega sonic power supply atfrequency f₃ first then frequency f₁ later, f₁ is higher than f₃ in step4. FIG. 9C shows another cleaning method of setting ultra/mega sonicpower supply at frequency f₃ first, frequency f₁ later and f₃ last, f₁is higher than f₃ in step 4. FIG. 9D shows another cleaning method ofsetting ultra/mega sonic power supply at frequency f₁ first, frequencyf₃ later and f₁ last, f₁ is higher than f₃ in step 4.

Similar to method shown in FIG. 9C, the ultra/mega sonic power can beset at frequency f₁ first, at frequency f₃ later and at frequency f₄ atlast in step 4, where f₄ is smaller than f₃, and f₃ is smaller than f₁.

Again similar to method shown in FIG. 9C, the ultra/mega sonic power canbe set at frequency f₄ first, at frequency f₃ later and at frequency f₁at last in step 4, where f₄ is smaller than f₃, and f₃ is smaller thanf₁

Again similar to method shown in FIG. 9C, the ultra/mega sonic power canbe set at frequency f₁ first, at frequency f₄ later and at frequency f₃at last in step 4, where f₄ is smaller than f₃, and f₃ is smaller thanf₁.

Again similar to method shown in FIG. 9C, the ultra/mega sonic power canbe set at frequency f₃ first, at frequency f₄ later and at frequency f₁at last in step 4, where f₄ is smaller than f₃, and f₃ is smaller thanf₁.

Again similar to method shown in FIG. 9C, the ultra/mega sonic power canbe set at frequency f₃ first, at frequency f₁ later and at frequency f₄at last in step 4, where f₄ is smaller than f₃, and f₃ is smaller thanf₁.

Again similar to method shown in FIG. 9C, the ultra/mega sonic power canbe set at frequency f₄ first, at frequency f₁ later and at frequency f₃at last in step 4, where f₄ is smaller than f₃, and f₃ is smaller thanf₁.

FIGS. 10A to 10B show another method to achieve a damage freeultra/mega-sonic cleaning on a wafer with patterned structure bymaintaining a stable bubble cavitation in according to the presentinvention. FIG. 10A shows waveform of power supply outputs, and FIG. 10Bshows the temperature curve corresponding to each cycle of cavitation.Operation process steps according to the present invention are disclosedas follows:

Step 1: Put ultra/mega sonic device adjacent to surface of wafer orsubstrate set on a chuck or tank;

Step 2: Fill chemical liquid or gas doped water between wafer and theultra/mega sonic device;

Step 3: Rotate chuck or oscillate wafer;

Step 4: Set power supply at frequency f₁ and power P₁;

Step 5: Before temperature of gas and vapor inside bubble reachesimplosion temperature T_(i), (total time τ₁ elapes), set power supplyoutput at frequency f₁ and power P₂, and P₂ is smaller than P₁.Therefore the temperature of gas inside bubble start to cool down sincethe temperature of liquid or water is much lower than gas temperature.

Step 6: After temperature of gas inside bubble decreases to certaintemperature close to room temperature T₀ or time (zero power time) reachτ₂, set power supply at frequency f₁ and power P₁ again.

Step 7: repeat Step 1 to Step 6 until wafer is cleaned.

In step 6, the temperature of gas inside bubble can not be cooled downto room temperature due to power P₂, there should be a temperaturedifference ΔT₂ existing in later stage of τ₂ time zone, as shown in FIG.10B.

FIGS. 11A to 11B show another embodiment of wafer cleaning method usinga ultra/mega sonic device according to the present invention. The methodis similar to that shown in FIG. 10A, except in step 5 settingultra/mega sonic power at frequency f₂ and power P₂, where f₂ is lowerthan f₁ and P₂ is less than P₁. Since f₂ is lower than f₁, thetemperature of gas or vapor inside bubble increasing faster, thereforethe P2 should be set significantly less than P1, better to be 5 or 10times less in order to reduce temperature of gas and or vapor insidebubble.

FIGS. 12A to 12B show another embodiment of wafer cleaning method usinga ultra/mega sonic device according to the present invention. The methodis similar to that shown in FIG. 10A, except in step 5 settingultra/mega sonic power at frequency f₂ and power P₂, where f₂ is higherthan f₁, and P₂ is equal to P₁.

FIGS. 13A to 13B show another embodiment of wafer cleaning method usinga ultra/mega sonic device according to the present invention. The methodis similar to that shown in FIG. 10A, except in step 5 settingultra/mega sonic power at frequency f₂ and power P₂, where f₂ is higherthan f₁, and P₂ is less than P₁.

FIGS. 14A-14B shows another embodiment of wafer cleaning method using aultra/mega sonic device according to the present invention. The methodis similar to that shown in FIG. 10A, except in step 5 settingultra/mega sonic power at frequency f₂ and power P₂, where f₂ is higherthan f₁, and P₂ is higher than P₁. Since f₂ is higher than f₁, thetemperature of gas or vapor inside bubble increasing slower, thereforethe P2 can be slightly higher than P1, but must make sure thetemperature of gas and vapor inside bubbler decreases in time zone τ₂comparing to temperature zone τ₁, as shown in FIG. 14B

FIGS. 4A and 4B show that patterned structure is damaged by the violentmicro jet. FIGS. 15A and 15B show that the stable cavitation can alsodamage the patterned structure on wafer. As bubble cavitation continues,the temperature of gas and vapor inside bubble increases, therefore sizeof bubble 15046 also increases as shown in FIG. 15A. When size of bubble15048 becomes larger than dimension of space W in patterned structure asshown in FIG. 15B, the expansion force of bubble cavitation can damagethe patterned structure 15034 as shown in FIG. 15C. Another cleaningmethod according to the present invention are disclosed as follows:

Step 1: Put ultra/mega sonic device adjacent to surface of wafer orsubstrate set on a chuck or tank;

Step 2: Fill chemical liquid or gas doped water between wafer and theultra/mega sonic device;

Step 3: Rotate chuck or oscillate wafer;

Step 4: Set power supply at frequency f₁ and power P₁;

Step 5: Before size of bubble reaches the same dimension of space W inpatterned structures (time τ₁ elapse), set power supply output to zerowatts, therefore the temperature of gas inside bubble starts to cooldown since the temperature of liquid or water is much lower than gastemperature;

Step 6: After temperature of gas inside bubble continues to reduce(either it reaches room temperature T₀ or time (zero power time) reachτ₂, set power supply at frequency f₁ power P₁ again;

Step 7: repeat Step 1 to Step 6 until wafer is cleaned;

In step 6, the temperature of gas inside bubble is not necessary to becooled down to room temperature, it can be any temperature, but betterto be significantly lower than implosion temperature T_(i). In the step5, bubble size can be slightly larger than dimension of patternedstructures as long as bubble expansion force does not break or damagethe patterned structure. The time τ₁ can be determined experimentally byusing the following method:

Step 1: Similar to Table 1, choosing 5 different time τ₁ as design ofexperiment (DOE) conditions,

Step 2: choose time τ₂ at least 10 times of τ₁, better to be 100 timesof τ₁ at the first screen test

Step 3: fix certain power P₀ to run above five conditions cleaning onspecific patterned structure wafer separately. Here, P₀ is the power atwhich the patterned structures on wafer will be surely damaged whenrunning on continuous mode (non-pulse mode).

Step 4: Inspect the damage status of above five wafers by SEMS or waferpattern damage review tool such as AMAT SEM vision or Hitachi IS3000,and then the damage time τ_(i) can be located in certain range.

Step 1 to 4 can be repeated again to narrow down the range of damagetime τ_(d). After knowing the damage time τ_(d), the time τ₁ can be setat a value smaller than 0.5 τ_(d) for safety margin.

All cleaning methods described from FIG. 7 to FIG. 14 can be applied inor combined with the method described in FIG. 15 .

FIG. 16 shows a wafer cleaning apparatus using a ultra/mega sonicdevice. The wafer cleaning apparatus consists of wafer 16010, waferchuck 16014 being rotated by rotation driving mechanism 16016, nozzle16064 delivering cleaning chemicals or de-ionized water 16060,ultra/mega sonic device 16062 coupled with nozzle 16064, and ultra/megasonic power supply. Ultra/mega sonic wave generated by ultra/mega sonicdevice 16062 is transferred to wafer through chemical or water liquidcolumn 16060. All cleaning methods described from FIG. 7 to FIG. 15 canbe used in cleaning apparatus described in FIG. 16 .

FIG. 17 shows a wafer cleaning apparatus using a ultra/mega sonicdevice. The wafer cleaning apparatus consists of wafers 17010, acleaning tank 17074, a wafer cassette 17076 holding the wafers 17010 andbeing held in the cleaning tank 17074, cleaning chemicals 17070, aultra/mega sonic device 17072 attached to outside wall of the cleaningtank 17074, and a ultra/mega sonic power supply. At least one inletfills the cleaning chemicals 17070 into the cleaning tank 17074 toimmerse the wafers 17010. All cleaning methods described from FIG. 7 toFIG. 15 can be used in cleaning apparatus described in FIG. 17 .

FIGS. 18A to 18C show another embodiment of wafer cleaning method usinga ultra/mega sonic device according to the present invention. The methodis similar to that shown in FIG. 7A, except in Step 5: Beforetemperature of gas and vapor inside bubble reaches implosion temperatureT_(i), (or time reach τ₁<τ_(i) as being calculated by equation (11)),set power supply output to a positive value or negative DC value to holdor stop ultra/mega sonic device to vibrate, therefore the temperature ofgas inside bubble start to cool down since the temperature of liquid orwater is much lower than gas temperature. The positive value of negativevalue can be bigger, equal to or smaller than power P₁.

FIG. 19 shows another embodiment of wafer cleaning method using aultra/mega sonic device according to the present invention. The methodis similar to that shown in FIG. 7A, except in Step 5: Beforetemperature of gas and vapor inside bubble reaches implosion temperatureT_(i), (or time reach τ₁<τ_(i) as being calculated by equation (11)),set power supply output at the frequency same as f₁ with reverse phaseto f₁ to quickly stop the cavitation of bubble. Therefore thetemperature of gas inside bubble start to cool down since thetemperature of liquid or water is much lower than gas temperature. Thepositive value of negative value can be bigger, equal or less than powerP₁. During above operation, the power supply output can be set at afrequency different from frequency f₁ with reverse phase to f₁ in orderto quickly stop the cavitation of bubble.

As shown in FIG. 20A to FIG. 20D, the bubbles 20012 are in the status ofbelow the saturation point in the feature of vias 20034 or trenches20036 on a substrate 20010, so as to increase the fresh chemicalexchange in the vias 20034 or trenches 20036 due to the bubblecavitation inside the features and also increase the removal ofimpurities such as residues and particles from the features. Thesaturation point R_(s) is defined by the largest amount of bubblesinside the features of vias, trenches or recessed areas. Over thesaturation point, the chemical liquid is blocked by the bubbles insidethe feature and hardly reaches to the bottom or side walls of thefeatures of vias and trenches, so that the cleaning performance of thechemical liquid is influenced. While below the saturation point, thechemical liquid has enough feasibility inside the features of vias ortrenches, and a good cleaning performance is achieved.

Below the saturation point, the ratio R of total bubbles volume V_(B) tothe volume of via or trench, or recessed space V_(VTR) is:R=V _(B) /V _(VTR) <R _(s)

And at or above the saturation point R_(s), the ratio R of total bubblesvolume V_(B) to the volume of via or trench, or recessed space V_(VTR)is:R=V _(B) /V _(VTR) =R _(s)

The volume of the total bubbles in the features of vias, trenches orrecessed space: V_(B)=Nv_(b)

Wherein N is the total bubble numbers in the features and v_(b) isaveraged single bubble volume.

As shown in FIG. 20E to FIG. 20H, the size of bubble 20012 expanded bythe ultra/mega sonic device is gradually to a certain volume, whichresults in the ratio R of total bubbles volume V_(B) to the volume ofvia, trench or recessed space V_(VTR) is closed to or above thesaturation point R_(s). It leads to the expanded bubble 20012 blockingin the vias or trenches, where is the path of chemical exchanges andimpurities removal. In the case, the megasonic power cannot thoroughlytransfer into the vias or trenches to reach their bottom and sidewall,meanwhile, the particles, residues and other impurities 20048 trapped inthe vias or trenches cannot go out efficiently. This case easily occursas the critical dimension W1 decreasing smaller, and the bubbles in thefeatures of vias and trenches intends to be saturated after beingexpanded.

As shown in FIG. 20I to FIG. 20J, the size of bubble 20012 is expandedby the ultra/mega sonic device within a limitation, and the ratio R oftotal bubbles volume V_(B) to the volume of via, trench or recessedspace V_(VTR) is much below the saturation point. The fresh chemical20047 exchanges freely in the vias or trenches due to the bubblecavitation inside the features to achieve a good cleaning performance,meanwhile, the impurities 20048 such as residues and particles go out ofthe features of vias, trenches and recessed space.

Due to the total bubbles in the features is related to the bubblenumbers and the bubble size in the features of vias and treches, thecontrol of bubble size expanded by the cavitation is critical for thecleaning performance in the high aspect ratio features cleaning process.

As shown in FIG. 21A to FIG. 21D, after the first cycle of cavitationfinishes, the volume of V₁ of gas in bubble is compressed to a minimumsize smaller than V₀ during positive sonic power working on it, and thevolume of V₂ of gas in bubble will be returned back during the negativesonic power working on it. However, the temperature T₂ in the bubblewith the volume of V₂ is higher than the temperature T₀ in the bubblewith the volume of V₀, as shown in FIG. 21B, so that the volume of V₂ isbigger than the volume of V₀ due to some liquid molecules surroundingbubble will evaporate under the high temperature. And the volume of V₃by the second compression of the bubble is somewhere between V₁ and V₂,as shown in FIG. 21B. And V₁, V₂ and V₃ can be expressed asV ₁ =V ₀ −ΔV  (12)V ₂ =V ₁ +δV  (13)V ₃ =V ₂ −ΔV=V ₁ +δV−ΔV=V ₀ −ΔV+δV−ΔV=V ₀ +δV−2ΔV  (14)

Where ΔV is volume compression of bubble after one time of compressiondue to positive pressure generated by ultra/mega sonic wave, and δV isvolume increase of the bubble after one time of expansion due tonegative pressure generated by ultra/mega sonic wave, and δV−ΔV isvolume increase due to temperature increment ΔT−δT as calculated inequation (5) after one time cycle.

After the second cycle of bubble cavitation, the size of bubble reachesto the larger bubble size during the temperature keeping increasing, thevolume of V₄ of gas and or vapor inside bubbler will beV ₄ =V ₃ +δV=V ₀ +δV−2ΔV+δV=V ₀+2(δV−ΔV)  (15)

When the third cycle of bubble cavitation, the volume V₅ of gas and/orvapor inside bubbler will beV ₅ =V ₄ −ΔV=V ₀+2(δV−ΔV)−ΔV=V ₀+2δV−3ΔV  (16)

Similarly, when the nth cycle of bubble cavitation reaches the minimumbubble size, the volume V_(2n-1) of gas and or vapor inside bubbler willbeV _(2n-1) =V ₀+(n−1)δV−nΔV=V ₀+(n−1)δV−nΔV  (17)

When the nth cycle of bubble cavitation finishes, the volume V_(2n) ofgas and/or vapor inside bubbler will beV _(2n) =V ₀ +n(δV−ΔV)  (18)

To restrict the volume of bubble into a desired volume V_(i), which is adimension with enough physical feasibility of movement or the bubblesstatus below the saturation point of cavitation or bubble density,rather than blocking the path of the chemical exchange in the featuresof vias, trenches or recessed areas, the cycle number n_(i) can bewritten as following:n _(i)=(V _(i) −V ₀ −ΔV)/(δV−ΔV)+1  (19)

From equation (19), the desired time τ_(i) to achieve the V_(i) can bewritten as following:

$\begin{matrix}{\tau_{i} = {{n_{i}t_{1}} = {{t_{1}\left( {{\left( {V_{i} - V_{0} - {\Delta V}} \right)/\left( {{\delta V} - {\Delta V}} \right)} + 1} \right)} = {{n_{i}/f_{1}} = {\left( {{\left( {V_{i} - V_{0} - {\Delta T}} \right)/\left( {{\delta V} - {\Delta V}} \right)} + 1} \right)/f_{1}}}}}} & (20)\end{matrix}$

Where, t₁ is cycle period, and f₁ frequency of ultra/mega sonic wave.

According to formulas (19) and (20), a desired cycle number n_(i) and atime τ_(i) to restrict the bubble dimension can be calculated.

It should be pointed that when the cycle number n of bubble cavitationincreases, the temperature of gas and liquid (water) vapor insidebubbler will increase, therefore more molecules on bubble surface willevaporate into inside of bubble, therefore the size of bubble 21082 willfurther increase and be bigger than value calculated by equation (18).In practical operation, since the bubble size will be determined byexperimental method to be disclosed later, therefore bubble sizeimpacted by the evaporation of liquid or water for bubble inner surfacedue to temperature increase will not be theoretically discussed indetail here. As the average single bubble volume keeping increasing, theratio R of total bubbles volume V_(B) to the volume of via, trench orrecessed space V_(VTR) increases from R₀ continuously, as shown in FIG.21D.

As the bubble volume increases, the diameter of bubble eventually willreach the same size or same order size of feature W1 such as via asshown in FIG. 20E and trench or recessed area as shown in FIG. 20G. Thenthe bubble inside via and trench will block ultra/mega sonic energyfurther get into the bottom of via and trench, especially when theaspect ratio (depth/width) is larger than 3 time or more. Thereforecontaminations or particles at bottom of such deep via or trench cannotbe effectively removed or cleaned.

In order to avoid the bubble growth up to a critical dimension to blockthe path of chemical exchanges in the features of vias or trenches,FIGS. 22A to 22D disclose a method to achieve an effective ultra/megasonic cleaning on a substrate with high aspect ratio features of vias ortrenches by maintaining a restricted size bubble cavitation according tothe present invention. FIG. 22A shows waveform of power supply outputs,and FIG. 22B shows the bubble volume curve corresponding to each cycleof cavitation, and FIG. 22C shows the bubble size expansion during eachcycle of cavitation, and FIG. 22D shows the curve of the ratio R oftotal bubbles volume V_(B) to the volume of via, trench or recessedspace V_(VTR). According toR=V _(B) /V _(VTR) =Nv _(b) /V _(VTR),

the ratio R of total bubbles volume V_(B) to the volume of via, trenchor recessed space V_(VTR) increases from R₀ to R_(n), where the averagesingle bubble volume being expanded by the sonic cavitation after acertain cycle number n, in the time of τ₁. And the R_(n) is controlledbelow the saturation point R_(s),R _(n) =V _(B) /V _(VTR) −Nv _(b) /V _(VTR) <Rs.

And the ratio R of total bubbles volume V_(B) to the volume of via,trench or recessed space V_(VTR) decreases from R_(n) to R₀, where theaverage single bubble volume return to original size in the coolingprocess in the time of τ₂.

Operation process steps to avoid bubble size growth up according to thepresent invention are disclosed as follows:

Step 1: Put ultra/mega sonic device adjacent to surface of substrate orsubstrate set on a chuck or tank;

Step 2: Fill chemical liquid or gas (hydrogen, nitrogen, oxygen, or CO₂)doped water between substrate and the ultra/mega sonic device;

Step 3: Rotate chuck or oscillate substrate;

Step 4: Set power supply at frequency f₁ and power P₁;

Step 5: After the volume of bubble expands to a certain volume V_(n) ordiameter w, (or time reach τ₁), set power supply output to zero watts,therefore the volume of gas inside bubble start to shrink down since thetemperature of liquid or water cooling down the gas temperature;

Step 6: After the volume of bubble decreases to original volume whilethe gas temperature decreasing to room temperature T₀ or time (zeropower time) reaches τ₂, set power supply at frequency f₁ and power P₁again;

Step 7: repeat Step 1 to Step 6 until substrate is cleaned.

In step 5, the expanded bubble's volume of V_(n) or diameter w is notnecessary to be restricted to be smaller than the dimension V_(i) orfeature size w1 that blocking the features of vias or trenches. It canbe certain volume above the V_(i), but better to be smaller than thedimension V_(i) in order to obtain an effective cleaning with shortestprocess time. And the τ₁ is also not necessary to be restricted to besmaller than τ_(i), but better to be smaller than the τ_(i) as beingdefined in the equation (20).

In step 6, the volume of bubble is not necessary to shrink down to anoriginal volume. It can be certain volume above original volume, butbetter to be significantly smaller than the V_(i) to restrict bubblesize to get ultra/mega sonic power to be transmitted to the bottom offeatures such as via, trench, or recessed area.

FIG. 22B shows that the bubble is expanded into a big volume V_(n) bythe ultra/mega sonic power working on it during a time τ₁. At thisstate, the path of mass transfer is partially blocked. And then thefresh chemical cannot thoroughly transfer into the vias or trenches toreach their bottom and sidewall, meanwhile, the particles, residues andother impurities trapped in the vias or trenches cannot go outefficiently. But the state will alternate into the next state for bubbleshrinking: when the ultra/mega sonic power is off for cooling the bubbleduring a time τ₂ as shown in FIG. 22A. In this cooling state, the freshchemical has chance to transfer into the vias or trenches so as to cleantheir bottom and sidewall. When the ultra/mega sonic power is on in thenext on cycle, the particles, residues and other impurities can beremoved out of the vias or trenches by pull out force generated bybubble volume increment. If the two states are alternating in a cleaningprocess, it achieves a performance of an effective ultra/mega soniccleaning on a substrate with high aspect ratio features of vias ortrenches or recessed areas.

The cooling state in the time τ₂ plays a key role in this cleaningprocess. It should be defined precisely. And the τ1<τ_(i) time torestrict bubble size, is desired, and the definition of τ_(i) also ispreferred. The following method can determine the time τ₂ to shrinkbubble size during a cooling down state and time τ₁ to restrict thebubble expanded to the blockage size experimentally. The experiment isdone by using an ultra/mega sonic device coupling with a chemical liquidto clean a pattern substrate with small features of vias and trenches,where the traceable residues exist to evaluate the cleaning performance.

Step 1: choose a τ₁ which is big enough to block the features, which canbe calculation as τ_(i) based on the equation (20).

Step 2: choose different time τ₂ to run DOE. The selection of time τ₂ isat least 10 times of τ₁, better to be 100 times of τ₁ at the firstscreen test.

Step 3: Fix time τ₁ and fix certain power P₀ to run at least fiveconditions cleaning on specific patterned structure substrateseparately. Here, P₀ is the power at which the features of vias ortrenches on substrate will be surely not cleaned when running oncontinuous mode (non-pulse mode).

Step 4: Inspect the traceable residues status inside the features ofvias or trenches of above five substrates by SEMS or element analyzertool such as EDX.

The step 1 to step 4 can be repeated again to gradually shorten the timeτ₂ till the traceable residues inside the features of vias or trenchesare observed. As the time τ₂ is shorten, the volume of bubble cannotshrink down enough, which will gradually block the features andinfluence the cleaning performance. This time is called critical coolingtime τ_(c). After knowing critical cooling time τ_(c), the time τ₂ canbe set at value larger than 2τ_(c) to gain safety margin.

A more detail example is shown as follows:

Step 1: choosing 10 different time τ₁ as design of experiment (DOE)conditions, such as τ₁₀, 2τ₁₀, 4τ₁₀, 8τ₁₀, 16τ₁₀, 32τ₁₀, 64τ₁₀, 128τ₁₀,256τ₁₀, 512τ₁₀, as shown in Table 3;

Step 2: choosing time τ₂ at least 10 times of 512τ₁₀, better to be 20times of 512τ₁₀ at the first screen test, as shown in Table 3;

Step 3: fixing certain power P₀ to run above ten conditions cleaning onspecific patterned structure substrate separately. Here, P₀ is the powerat which the features of vias or trenches on substrate will be surelynot cleaned when running on continuous mode (non-pulse mode).

TABLE 3 Substrate# 1 2 3 4 5 6 7 8 9 10 τ₁ τ₁₀ 2τ₁₀ 4τ₁₀ 8τ₁₀ 16τ₁₀32τ₁₀ 64τ₁₀ 128τ₁₀ 256τ₁₀ 512τ₁₀ τ₂ 5120τ₁₀ 5120τ₁₀ 5120τ₁₀ 5120τ₁₀5120τ₁₀ 5120τ₁₀ 5120τ₁₀ 5120τ₁₀ 5120τ₁₀ 5120τ₁₀ Power P0 P0 P0 P0 P0 P0P0 P0 P0 P0 Process Time T₀ T₀ T₀ T₀ T₀ T₀ T₀ T₀ T₀ T₀ Clean Status 1 23 4 5 6 5 4 4 3 of Features

Step 4: Using above conditions as shown in Table 3 to process 10substrates with features of vias or trenches post plasma etching. Thereason to choose the post plasma etched substrate is that the polymersgenerated during etching process are formed on sidewall of trench andvia. Those polymers formed on the bottom or side wall of via aredifficulty to remove by a conventional method. Then inspect the cleaningstatus of features of vias or trenches on the ten substrates by SEMSwith crossing section of substrates. The data are shown in Table 3. Fromthe Table 3, the cleaning effect reaches the best point of 6 atτ₁=32τ₁₀, therefore the optimum time τ₁ is 32τ₁₀.

If there is no peak to be found, then the step 1 to step 4 with boardtime setting of τ₁ can be repeated again to find the time τ₁. After findthe initial τ₁, then step 1 to step 4 with time setting close to τ₁ canbe repeated again to narrow down the range of time After knowing thetime τ_(i), the time τ₂ can be optimized by reducing the time τ₂ from512 τ₂ to a value till the cleaning effect is reduced. A detailprocedure is disclosed as follows Table 4:

TABLE 4 Substrate# 1 2 3 4 5 6 7 8 τ₁ 32τ₁₀ 32τ₁₀ 32τ₁₀ 32τ₁₀ 32τ₁₀32τ₁₀ 32τ₁₀ 32τ₁₀ τ₂ 4096τ₁₀ 2048τ₁₀ 1024τ₁₀ 512τ₁₀ 256τ₁₀ 128τ₁₀ 64τ₁₀32τ₁₀ Power P0 P0 P0 P0 P0 P0 P0 P0 Process T₀ T₀ T₀ T₀ T₀ T₀ T₀ T₀ TimeClean 3 4 5 6 7 6 5 3 Status of Features

From the Table 4, the cleaning effect reaches the best point of 7 atτ₂=256τ₁₀, therefore the optimum time τ₂ is 256τ₁₀.

FIGS. 23A to 23C show another embodiment of substrate cleaning methodusing a ultra/mega sonic device according to the present invention. Themethod is similar to that shown in FIGS. 22A to 22D, except that poweris still on for period of mτ₁ even the cavitation reaches a saturationpoint Rs. Here, m can be number from 0.1 to 100, preferred 2, which isdepending on via and trench structure and chemicals, and it need to beoptimized by experiment explained in embodiment as FIGS. 22A to 22D.

Method and apparatus disclosed in FIG. 8 to FIG. 14 , and FIG. 16 toFIG. 19 can be applied in embodiments as shown in FIG. 22 and FIG. 23 ,it will not be described here again.

Generally speaking, an ultra/mega sonic wave with the frequency between0.1 MHz˜10 MHz may be applied to the method disclosed in the presentinvention.

As described above, the present invention discloses a method foreffectively cleaning vias, trenches or recessed areas on a substrateusing ultra/mega sonic device, comprising: applying liquid into a spacebetween a substrate and an ultra/mega sonic device; setting anultra/mega sonic power supply at frequency f₁ and power P₁ to drive saidultra/mega sonic device; after the ratio of total bubbles volume tovolume inside vias, trenches or recessed areas on the substrateincreasing to a first set value, setting said ultra/mega sonic powersupply at frequency f₂ and power P₂ to drive said ultra/mega sonicdevice; after the ratio of total bubbles volume to volume inside thevias, trenches or recessed areas reducing to a second set value, settingsaid ultra/mega sonic power supply at frequency f₁ and power P₁ again;repeating above steps till the substrate being cleaned.

The first set value is below the cavitation saturation point. The secondset value is much lower than the cavitation saturate point. Thetemperature inside bubble cooling down results in the ratio of totalbubbles volume to volume inside the vias, trenches or recessed areasreducing to the second set value. The temperature inside bubble coolingdown to near temperature of said liquid.

At above embodiment, the first set value is a cavitation saturationpoint, and even after the ratio of total bubbles volume to volume insidevias, trenches or recessed areas on the substrate reaches to thecavitation saturation point, the ultra/mega sonic power supply is stillkept at frequency f₁ and power P₁ for period of mτ₁, here τ₁ is the timeto reach the cavitation saturation point, m is multiples of τ₁, which isa number between 0.1 to 100, preferred 2.

According to an embodiment, the present invention discloses an apparatusfor effectively cleaning vias, trenches or recessed areas on a substrateusing an ultra/mega sonic device. The apparatus includes a chuck, anultra/mega sonic device, at least one nozzle, an ultra/mega sonic powersupply and a controller. The chuck holds a substrate. The ultra/megasonic device is positioned adjacent to the substrate. The at least onenozzle injects chemical liquid on the substrate and a gap between thesubstrate and the ultra/mega sonic device. The controller sets theultra/mega sonic power supply at frequency f₁ and power P₁ to drive theultra/mega sonic device; after the ratio of total bubbles volume tovolume inside vias, trenches or recessed areas on the substrateincreasing to a first set value, the controller setting the ultra/megasonic power supply at frequency f₂ and power P₂ to drive the ultra/megasonic device; after the ratio of total bubbles volume to volume insidethe vias, trenches or recessed areas reducing to a second set value, thecontroller setting the ultra/mega sonic power supply at frequency f₁ andpower P₁ again; repeating above steps till the substrate being cleaned.

According to another embodiment, the present invention discloses anapparatus for effectively cleaning vias, trenches or recessed areas on asubstrate using an ultra/mega sonic device. The apparatus includes acassette, a tank, an ultra/mega sonic device, at least one inlet, anultra/mega sonic power supply and a controller. The cassette holds atleast one substrate. The tank holds the cassette. The ultra/mega sonicdevice is attached to outside wall of the tank. At least one inlet isused for filling chemical liquid into the tank to immerse the substrate.The controller sets the ultra/mega sonic power supply at frequency f₁and power P₁ to drive the ultra/mega sonic device; after the ratio oftotal bubbles volume to volume inside vias, trenches or recessed areason the substrate increasing to a first set value, the controller settingthe ultra/mega sonic power supply at frequency f₂ and power P₂ to drivethe ultra/mega sonic device; after the ratio of total bubbles volume tovolume inside the vias, trenches or recessed areas reducing to a secondset value, the controller setting the ultra/mega sonic power supply atfrequency f₁ and power P₁ again; repeating above steps till thesubstrate being cleaned.

According to another embodiment, the present invention discloses anapparatus for effectively cleaning vias, trenches or recessed areas on asubstrate using an ultra/mega sonic device. The apparatus includes achuck, an ultra/mega sonic device, a nozzle, an ultra/mega sonic powersupply and a controller. The chuck holds a substrate. The ultra/megasonic device coupled with a nozzle is positioned adjacent to thesubstrate. The nozzle injects chemical liquid on the substrate. Thecontroller sets the ultra/mega sonic power supply at frequency f₁ andpower P₁ to drive the ultra/mega sonic device; after the ratio of totalbubbles volume to volume inside vias, trenches or recessed areas on thesubstrate increasing to a first set value, the controller setting theultra/mega sonic power supply at frequency f₂ and power P₂ to drive theultra/mega sonic device; after the ratio of total bubbles volume tovolume inside the vias, trenches or recessed areas reducing to a secondset value, the controller setting the ultra/mega sonic power supply atfrequency f₁ and power P₁ again; repeating above steps till thesubstrate being cleaned.

Although the present invention has been described with respect tocertain embodiments, examples, and applications, it will be apparent tothose skilled in the art that various modifications and changes may bemade without departing from the invention.

What is claimed is:
 1. An apparatus for cleaning a semiconductor wafercomprising features of patterned structures, the apparatus comprising: awafer holder configured to hold the semiconductor wafer; an inletconfigured to apply liquid on the semiconductor wafer; a transducerconfigured to deliver acoustic energy to the liquid; a power supply ofthe transducer; and a controller for the power supply comprising atimer, the controller being configured to control the transducer basedon the timer to: deliver acoustic energy to the liquid at a firstfrequency value and a first power level value for a predetermined firsttime period, wherein sizes of bubbles inside the features increaseduring the first time period, and deliver acoustic energy to the liquidat a second frequency value and a second power level value for apredetermined second time period, wherein sizes of bubbles inside thefeatures decrease during the second time period, wherein the controlleris configured to alternately apply the first and second time periods oneafter another for a predetermined number of cycles, and wherein thefirst time period and the second time period are determined based on aration (R) of total bubble volume (V_(B)) to volume (V_(VTR)) insidevias, trenches, or recessed areas on the semiconductor wafer.
 2. Theapparatus of claim 1, wherein the wafer holder comprises a rotatingchuck.
 3. The apparatus of claim 1, wherein the wafer holder comprises acassette submerged in a cleaning tank.
 4. The apparatus of claim 1,wherein the inlet comprises a nozzle.
 5. The apparatus of claim 1,wherein the transducer is connected to the inlet and imparts acousticenergy to the liquid flowing through the inlet.
 6. The apparatus ofclaim 1, wherein the first time period is determined as a time periodthat achieves the highest number of cleaned features.
 7. The apparatusof claim 1, wherein the second time period is determined as a timeperiod that achieves the highest number of cleaned features.
 8. Theapparatus of claim 1, wherein the first time period ends prior to atleast one of the features being blocked by the bubbles.
 9. The apparatusof claim 1, wherein the first time period ends after at least one of thefeatures being blocked by the bubbles.
 10. The apparatus of claim 1,wherein the second power level value is lower than the first power levelvalue.
 11. The apparatus of claim 10, wherein the second power levelvalue is zero.
 12. The apparatus of claim 1, wherein the secondfrequency value is higher than the first frequency value.
 13. Theapparatus of claim 1, wherein acoustic energy in the second time periodis in antiphase to acoustic energy in the first time period.
 14. Theapparatus of claim 1, wherein the first frequency value is equal to thesecond frequency value, while the first power level value is higher thanthe second power level value.
 15. The apparatus of claim 1, wherein thefirst frequency value is higher than the second frequency value, whilethe first power level value is higher than the second power level value.16. The apparatus of claim 1, wherein the first frequency value is lowerthan the second frequency value, while the first power level value isequal to the second power level value.
 17. The apparatus of claim 1,wherein the first frequency value is lower than the second frequencyvalue, while the first power level value is higher than the second powerlevel value.
 18. The apparatus of claim 1, wherein the first frequencyvalue is lower than the second frequency value, while the first powerlevel value is lower than the second power level value.
 19. Theapparatus of claim 1, wherein the first power level value rises duringthe first time period.
 20. The apparatus of claim 1, wherein the firstpower level value falls during the first time period.
 21. The apparatusof claim 1, wherein the first power level value both rises and fallsduring the first time period.
 22. The apparatus of claim 1, wherein thefirst frequency value changes from a higher value to a lower valueduring the first time period.
 23. The apparatus of claim 1, wherein thefirst frequency value changes from a lower value to a higher valueduring the first time period.
 24. The apparatus of claim 1, wherein thefirst frequency value changes from a lower value to a higher value andthen back to the lower value during the first time period.
 25. Theapparatus of claim 1, wherein the first frequency value changes from ahigher value to a lower value and then back to the higher value duringthe first time period.
 26. The apparatus of claim 1, wherein the firstfrequency value is set as f₁ first, f₃ later and fa at last during thefirst time period, where f₄ is smaller than f₃, and f₃ is smaller thanf₁.
 27. The apparatus of claim 1, wherein the first frequency value isset as f₄ first, f₃ later and f₁ at last during the first time period,where f₄ is smaller than f₃, and f₃ is smaller than f₁.
 28. Theapparatus of claim 1, wherein the first frequency value is set as f₁first, f₄ later and f₃ at last during the first time period, where f₄ issmaller than f₃, and f₃ is smaller than f₁.
 29. The apparatus of claim1, wherein the first frequency value is set as f₃ first, f₄ later and f₁at last during the first time period, where f₄ is smaller than f₃, andf₃ is smaller than f₁.
 30. The apparatus of claim 1, wherein the firstfrequency value is set as f₃ first, f₁ later and f₄ at last during thefirst time period, where f₄ is smaller than f₃, and f₃ is smaller thanf₁.
 31. The apparatus of claim 1, wherein the first frequency value isset as f₄ first, f₁ later and f₃ at last during the first time period,where f₄ is smaller than f₃, and f₃ is smaller than f₁.
 32. Theapparatus of claim 1, wherein the second frequency value is zero and thesecond power level value remains a constant positive value during thesecond time period.
 33. The apparatus of claim 1, wherein the secondfrequency value is zero and the second power level value remains aconstant negative value during the second time period.
 34. The apparatusof claim 1, wherein the features comprise vias or trenches having depthto width ratios of at least
 3. 35. The apparatus of claim 1, wherein adevice manufacturing node of the semiconductor wafer is no more than 16nanometers.
 36. The apparatus of claim 1, wherein the wafer holder isfurther configured to rotate the wafer with respect to the transducer asacoustic energy is delivered.
 37. The apparatus of claim 1, wherein thesecond time period ends after a ratio of total bubble volume inside thefeatures falls much lower than a cavitation saturation point.
 38. Theapparatus of claim 1, wherein the first time period ends before a ratioof total bubble volume inside the features reaches a cavitationsaturation point.
 39. The apparatus of claim 1, wherein the first timeperiod ends when a ratio of total bubble volume inside the featuresreaches a cavitation saturation point.
 40. The apparatus of claim 1,wherein a duration of the first time period is mτ₁, where τ₁, is a timefor a ratio of total bubble volume inside the features reaches acavitation saturation point.
 41. The apparatus of claim 40, wherein m isa value between 0.1 to
 100. 42. The apparatus of claim 1, whereintemperatures inside the bubbles decrease in the second time period. 43.The apparatus of claim 42, wherein temperatures inside the bubbledecrease to a temperature of said liquid in the second time period. 44.The apparatus of claim 1, wherein the first time period is shorter than2,000 times of a cycle period of the first frequency value.
 45. Theapparatus of claim 1, wherein the first time period is shorter than((V_(i)−V₀−ΔV)/(ΔV−δV)+1)/f₁, where V_(i) is a desired volume, is adesired volume, V₀ is an original volume, ΔV is a volume compression ofthe bubble after one time of compression, δV is a volume increase of thebubble after one time of expansion, and f1 is the first frequency value.46. A controller for a power supply of a transducer comprising a timer,the controller being configured to control the transducer based on thetimer to: deliver acoustic energy to liquid applied on a semiconductorwafer at a first frequency value and a first power level value for apredetermined first time period, wherein sizes of bubbles insidefeatures of patterned structures of the semiconductor wafer increaseduring the first time period; and deliver acoustic energy to the liquidat a second frequency value and a second power level value for apredetermined second time period, wherein sizes of bubbles insidefeatures decrease during the second time period, wherein the controlleris configured to alternately apply the first and second time periods oneafter another for a predetermined number of cycles, and wherein thefirst time period and the second time period are determined based on aratio (R) of total bubble volume (V_(B)) to volume (V_(VTR)) insidevias, trenches, or recessed areas on the semiconductor wafer.
 47. Thecontroller of claim 46, wherein the first time period is determined as atime period that achieves the highest number of cleaned features. 48.The controller of claim 46, wherein the second time period is determinedas a time period that achieves the highest number of cleaned on thefeatures.
 49. The controller of claim 46, wherein the first time periodends prior to at least one of the features being blocked by the bubbles.50. The controller of claim 46, wherein the first time period ends afterat least one of the features being blocked by the bubbles.
 51. Thecontroller of claim 46, wherein the second power level value is lowerthan the first power level.
 52. The controller of claim 51, wherein thesecond power level value is zero.